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The effect of electronically steering a phased array ultrasound transducer on near-field tissue heating
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10.1118/1.3618729
/content/aapm/journal/medphys/38/9/10.1118/1.3618729
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/9/10.1118/1.3618729

Figures

Image of FIG. 1.
FIG. 1.

Schematic of the experimental setup. The phased array transducer, tissue-mimicking phantom, 3D segmented EPI volume location, and scan path patterns in an x-y plane projection are all shown. (a) Nine-point scanning pattern, Δx = Δy = 1 cm. (b) Twelve-point, 16-mm diameter circular scanning pattern.

Image of FIG. 2.
FIG. 2.

The experimental and simulated thermal dose maps accumulated in a tissue-mimicking phantom for the nine-point raster scan with the focal plane of the trajectory located at z = 14 cm. The electronically steered, (a) experimental, and (b) simulated thermal dose maps [33–49 W] are shown at distances measured from the transducer’s distal face. (The acoustic power ranges for each are given in square parentheses.) The mechanically steered (c) experimental and (d) simulated thermal dose maps [33 W] are also shown. (e) Simulated thermal dose maps for the fully sampled transducer electronically steered. The scale bar for the dose maps is 0–50 CEM43 °C at z = 14.0 and 14.4 cm, 0–20 CEM43 °C for (a) and (b) and 0–10 CEM43 °C for (c)–(e) at z = 11.4–13.0 cm.

Image of FIG. 3.
FIG. 3.

Superposition of the simulated power deposition patterns used in the thermal simulations presented in Figs. 2 and 4 for the nine-point raster trajectory. (a)–(c) Superimposed beam patterns for the electronically steered trajectory for (a) an axial slice, (b) transverse slice 1.5 cm proximal to the focal plane, and (c) transverse slice 2.5 cm proximal to the focal plane. (d)–(f) Superimposed beam patterns for the mechanically steered trajectory for (d) an axial slice, (e) transverse slice 1.5 cm proximal to the focal plane and (f) transverse slice 2.5 cm proximal to the focal plane. (g)–(i) Superimposed beam patterns for the fully sampled transducer electronically steered trajectory for (g) an axial slice, (h) transverse slice 1.5 cm proximal to the focal plane and (i) transverse slice 2.5 cm proximal to the focal plane. All scale bars have the units of Watts per cubic meter.

Image of FIG. 4.
FIG. 4.

Log plot of the mean of the 25 voxels with the highest thermal dose (CEM43 °C) accumulated in planes perpendicular to the ultrasound beam’s axis during the nine-position raster trajectory as a function of distance from the transducer face. The error bars for the experimental data at each point represent one standard deviation (n = 3). The focal plane is located at z = 14 cm. Both simulated and experimental data are shown for both electronic and mechanical steering. The simulation of the electronically steered fully sampled (FS) transducer is also shown.

Image of FIG. 5.
FIG. 5.

Superposition of the simulated power deposition patterns used in the thermal simulations presented in Figs. 6 and 7 for the 12 point, 16 mm circular trajectory. (a)–(c) Superimposed beam patterns for the electronically steered trajectory for (a) an axial slice, (b) transverse slice 1.5 cm proximal to the focal plane, and (c) transverse slice 2.5 cm proximal to the focal plane. (d)–(f) Superimposed beam patterns for the mechanically steered trajectory for (d) an axial slice, (e) transverse slice 1.5 cm proximal to the focal plane and (f) transverse slice 2.5 cm proximal to the focal plane. (g)–(i) Superimposed beam patterns for the fully sample transducer electronically steered trajectory for (g) an axial slice, (h) transverse slice 1.5 cm proximal to the focal plane and (i) transverse slice 2.5 cm proximal to the focal plane. All scale bars have units of Watts per cubic meter.

Image of FIG. 6.
FIG. 6.

Thermal dose (in CEM43 °C) accumulated during the 16-mm circle trajectory in various x-y planes along the transducer’s axis for both electronically and mechanically steered trajectories. Electronically steered (a) experimental and (b) simulated data, (c) simulated mechanically steered data and (d) simulated electronically steered fully sampled transducer. The focal plane for the ultrasound beam is located at z = 13 cm. In all cases, the total sonication time was 60 s. The power for the electronically steered trajectory (both simulated and experimental) was 114 acoustic W to account for steering losses. The mechanically steered trajectory power input was 108 W.

Image of FIG. 7.
FIG. 7.

Mean of the 25 voxels with the highest thermal dose (CEM43 °C) accumulated in planes perpendicular to the transducer’s axis for the 16-mm circular trajectory. The focal plane is at 13 cm. Both experimental and simulated results are displayed for electronic steering, and simulated data for the mechanically steered trajectory, and the electronically steered fully sampled (FS) transducer. The error bars for the experimental data at each point represent one standard deviation (n = 3).

Image of FIG. 8.
FIG. 8.

Effect of perfusion on the mean of the 25 voxels with the highest thermal dose accumulated in planes perpendicular to the transducer’s axis for the 16-mm circle trajectory. Pennes’ perfusion values of 0,1, and 5 kg/m3-s are shown. The focal plane for the ultrasound beam is located at z = 13 cm.

Image of FIG. 9.
FIG. 9.

Mean of the 25 voxels with the highest power deposition Q as a function of distance from the transducer’s distal face for three different transducer configurations of (a) an unsteered beam at the geometric focus, (b) a beam steered 1 cm away from the transducer axially, and (c) a beam steered 1 cm off-axis in both the x and y transverse directions. The power deposition for each transducer is normalized to the mean power deposition in the peak 25 voxels at the geometric focus for transducer #1.

Tables

Generic image for table
TABLE I.

Tissue properties used in simulations.

Generic image for table
TABLE II.

Transducers analyzed and summary of results.

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/content/aapm/journal/medphys/38/9/10.1118/1.3618729
2011-08-10
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The effect of electronically steering a phased array ultrasound transducer on near-field tissue heating
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/9/10.1118/1.3618729
10.1118/1.3618729
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